chore: scaffold test hygiene — constant extraction, missing assertions, direct dcp.jsonc coverage

[yvonnedevlinrh]

Summary

Follow-up from PR #224 review. Addresses 3 LOW advisory findings and 1 pre-existing test gap, all scoped to internal/scaffold/scaffold_test.go (and one URL in internal/scaffold/assets/dcp.jsonc).

Tasks

1. Extract hardcoded asset count to named constant

The magic number 9 appears across 8+ test assertion sites. Each new embedded asset requires a mechanical find-and-replace.

• Add const expectedAssetCount = 9 (or similar) in scaffold_test.go
• Replace all hardcoded 9 count assertions with the constant

2. Complete TestRun_CreatesFiles expected file list

The on-disk existence check (line 48-56) enumerates only 7 of 9 files. Missing since before PR #224:

• Add ".opencode/agents/gaze-test-generator.md" to the expected list
• Add ".opencode/commands/gaze-fix.md" to the expected list

3. Add direct dcp.jsonc overwrite-on-diff coverage

TestRun_OverwriteOnDiff_ToolOwned modifies 2 .md tool-owned files and verifies restoration, but dcp.jsonc is only covered implicitly via count arithmetic.

• In the test's "modify on disk" section, also mutate .opencode/dcp.jsonc
• After third run, verify dcp.jsonc content matches the raw embedded asset (no marker)
• Update expected counts: 3 updated, 6 skipped (3 user-owned + 3 identical tool-owned)

4. Pin $schema URL (optional)

dcp.jsonc references master branch:

https://raw.githubusercontent.com/Opencode-DCP/opencode-dynamic-context-pruning/master/dcp.schema.json

A pinned commit SHA or version tag would be more stable. However, this is a DCP community convention for editor tooling — defer if upstream doesn't publish tagged releases.

• Check if DCP repo publishes tagged releases or pinnable refs
• If yes, pin to specific ref; if no, skip (document decision)

Scope

• Files: internal/scaffold/scaffold_test.go, optionally internal/scaffold/assets/dcp.jsonc
• Production code changes: None (test-only + optional asset URL)
• Spec required: No — test hygiene, no behavior change